Support latex package

Hello,

Sometimes, math-preview fails because it does not know some latex commands, e.g. the \sfrac{}{} environment or the \begin{align}...\end{align}. I checked for this latest that it exports well to pdf.

Also, in my org files I used to have some latex directives to define or redefine some latex commands. They seem to be ignored by math-preview.

More generally, how can I pass to math-preview, i.e. to the underlying mathjax, any latex package or user defined commands ?

Regards